1. Field of the Invention
The present invention relates to a radio base station apparatus that forms a wireless zone in a mobile communication system in which a terminal or a call occurring at a terminal is given different IP addresses for wireless zones. It also relates a base station controller that performs a channel control over a terminal visiting a wireless zone.
2. Description of the Related Art
In recent years, data terminals and communication terminals accessible to the Internet have spread rapidly. For radio transmission channels in next-generation mobile communication systems, use of the IP (Internet protocol) has been studied, because of its high compatibility with the Internet, for replacement the multiple access schemes which comply with the circuit switching system. Also, radio transmission channels and line transmission sections have become seamless step by step.
FIG. 6 shows the configuration of an exemplary mobile communication system in which different IP addresses are assigned for respective wireless zones.
As shown in FIG. 6, radio base stations 70-1 and 70-2 form overlapping wireless zones 81-1 and 81-2, respectively. A terminal 82 locates in one of the wireless zones 81-1 and 81-2, for example, in the wireless zone 81-1. The radio base stations 70-1 and 70-2 are connected to a base station controlling station 84 via communication links 83-1 and 83-2, respectively.
The radio base station 70-1 has the following components:                Antenna 71-1        Antenna duplexer 72-1 that is connected to the feeding point of the antenna 71-1.        Receiving part 73-1 that is connected to the reception output of the antenna duplexer 72-1.        Router 74-1 that is connected to the one end of an inter-office link provided between the radio base station 70-1 and an exchange (not shown), and to whose incoming route the output of the receiving part 73-1 is connected.        Transmitting part 77-1 that is connected in series to the outgoing route of the router 74-1 and whose output is connected to the transmission input of the antenna duplexer 72-1.        Controlling part 76-1 having input/output ports that are connected to the control terminals of the receiving part 73-1, the router 74-1, and the transmitting part 77-1, respectively, and a communication port that is connected to the one end of the above-mentioned communication link 83-1.        
The radio base station 70-2 has the same configuration as the radio base station 70-1. Therefore, the components of the radio base station 70-2 will be given the same reference symbols as those of the radio base station 70-1 except that the former will have a suffix “2” instead of a suffix “1,” and will not be described or shown in the drawings.
In the mobile communication system having the above configuration, the radio base stations 70-1 and 70-2 form wireless zones 81-1 and 81-2 that comply with a predetermined multiple access scheme and channel allocation, by cooperating with, via the respective communication links 83-1 and 83-2, the base station controlling station 84 performing a channel control and call setting in cooperation with the above-mentioned exchange.
Recognizing that a call that occurred at the terminal 82 has become a complete call during the course of such a channel control, the radio base station 70-1 assigns the terminal 82 a unique IP address (for the sake of simplicity, it is assumed here to be “192.168.0.2” and will be referred to as “first IP address”) that is not assigned to any other terminals or calls.
When the terminal 82 has moved to the overlap region of the wireless zones 81-1 and 81-2 before the complete call disappears, it issues a handover request to the radio base station 70-1 according to a prescribed channel control procedure (indicated by symbol (a) in FIG. 7).
The radio base station 70-1 receives the handover request at the antenna 71-1, the antenna duplexer 72-1, and the receiving part 73-1 and the controlling part 76-1 thereof forwards it to the base station controlling station 84 via the communication link 83-1 (indicated by symbol (b) in FIG. 7).
The base station controlling station 84 performs the following processing in response to the handover request:                Determines a wireless zone (hereinafter referred to as “transition destination wireless zone”; for the sake of simplicity, it is assumed to be the wireless zone 81-2) to which the terminal 82 should make a transition.        Determines a radio channel (hereinafter referred to as “transition destination radio channel”) that can be assigned by the radio base station 70-2 which forms the wireless zone 81-2 and that is not assigned to any terminal or call.        Sends, to the radio base station 70-2, via the communication link 83-2, a transmission start request for starting a transmission on the transition destination radio channel (indicated by symbol (c) in FIG. 7).        Sends, to the radio base station 70-1, via the communication link 83-1, a handover request confirmation that the terminal 82 should make a transition to the above transition destination radio channel (indicated by symbol (d) in FIG. 7).        
During the above processing, the base station controlling station 84 may cooperate with the radio base station 70-2 in any form.
In the radio base station 70-1, when recognizing the handover request confirmation, the controlling part 76-1 sends the handover request confirmation to the terminal 82 via the transmitting part 77-1, the antenna duplexer 72-1, and the antenna 71-1 (indicated by symbol (e) in FIG. 7).
When recognizing the handover request confirmation, the terminal 82 performs the following processing:                Performs a series of operations (hereinafter referred to simply as “radio channel establishment”) including synchronization establishment in the transition destination radio channel and a continuity check by cooperating, when necessary, with the radio base station 70-2 that forms the transition destination wireless zone (indicated by symbol (f) in FIG. 7).        When the radio channel establishment has completed normally, sends to the radio base station 70-2 a message called “binding update” which is an assignment request for a second IP address that complies with the transition destination wireless zone and is to replace the above-mentioned first IP address (indicated by symbol (g) in FIG. 7).        
The radio base station 70-2 sends the binding update message to the base station controlling station 84 via the communication link 83-2.
Recognizing the binding update message, the base station controlling station 84 performs the following processing:                Secures an IP address (for the sake of simplicity, it is assumed here to be “192.168.1.2”) as a second IP address by itself or in cooperation with the radio base station 70-2. The IP address is in such a value range that the radio base station 70-2 is allottable and is not assigned to any terminal or call (indicated by symbol (i) in FIG. 7). In the following description, for the sake of simplicity, it is assumed that the host address portions of the first IP address and the second IP address are defined under different subnet masks corresponding to the respective radio base stations 70-1 and 70-2 (wireless zones 81-1 and 81-2) so as to secure compatibility with the known mobile-IP that does not conform to the mobile communication and the radio transmission sufficiently.        Allows a relationship between the terminal 82 (or the transition destination channel assigned to the terminal 82) and the second IP address to be reflected in routing information held in the router 74-2 (indicated by symbol (j) in FIG. 7).        Sends a message “binding update confirmation” containing the second IP address to the terminal 82 via the communication link 83-2 and the radio base station 70-2 (indicated by symbol (k) in FIG. 7).        
The terminal 82 completes the handover by using, as one of the following, the second IP address contained in the binding update confirmation as an IP address that has been assigned in place of the first IP address (indicated by symbol (m) in FIG. 7):                Transmission source address that should be placed in the header of each packet that is sent from the terminal 82 itself.        Address that should be placed in the header of each of packets to be directed to the terminal 82 itself among packets received from the radio base station 70-2 via the transition destination radio channel.        
With the above processing, it is able to achieve a handover between the overlapping wireless zones 81-1 and 81-2 formed by the respective radio base stations 70-1 and 70-2 with high reliability, as long as the routers 74-1 and 74-2 of the radio base stations 70-1 and 70-2 are given proper pieces of routing information, and first and second IP addresses comply with those pieces of routing information.
The following documents disclose prior art techniques relating to the invention:    JP-A-2001-45534 (claims 4, 6, 8, and 9, paragraphs 0013, 0015, 0018, 0023, 0034, 0035, 0040-0042, 0044-0046, 0050, 0056-0058, 0060, 0063-0065, and 0067)    JP-A-2001-189954 (abstract, paragraph 0031)    JP-A-10-117167 (abstract, claim 1)    JP-A-11-122672 (claims 1-16)    JP-A-10-190633 (claim 1, paragraph 0001)    JP-T-10-509287 (abstract; the term “JP-T” as used herein means a published Japanese translation of a PCT patent application)    JP-A-2000-286898 (abstract, claim 1, paragraphs 0003 and 0016)
Incidentally, in the above prior art examples, a handover is attained by executing the second processing (indicated by symbols (g)-(m) in FIG. 7) for assignment of a second IP address that is to replace a first IP address after completion of the first processing (indicated by symbols (a)-(f) in FIG. 7) for realizing update of a physical radio channel.
That is, during such a handover process, every time the terminal 82 moves to a new wireless zone, it is given a new IP address as appropriate in accordance with a new radio channel that is physically different from an old one.
Therefore, the prior art examples enable transmission services of a variety of transmission information by using the IP; however, they cannot realize a diversity handover in accordance with substantially varying distances between the relative positions of the terminal 82 and the radio base stations 70-1 and 70-2 and according to the transmitting power control to solve the near-far problem of the CDMA scheme. Also, they cannot take advantage of merits of the CDMA scheme to maintain high, stable transmission quality of a radio transmission channel.